Resumen

Long-term continuous cropping of cotton had led to substantial agricultural losses. However, continuous cotton cropping could maintain high crop yields for many years in some areas. The composition and structure of soil nematode communities were investigated to explore the effect of continuous cropping and soil depths on these communities. Soil samples were collected at two soil depths (0-20 cm and 20-40 cm) from cotton fields with a history of 5, 10, 15 or 20 years of continuous cotton cropping in the Karamay region. The results showed that 36 genera were found. Significant differences in the numbers of total nematodes and trophic groups were observed among continuous cropping times. The highest number of total nematodes was observed at 20-40 cm depth under continuous 10-cropping years, and the lowest number at 20-40 cm depth under continuous 5-cropping years. There were significant soil depth effects on the density of fungivores and plant parasites. Continuous cropping effects on soil nematode communities could be refected by values of ecological indexes. Continuous cropping times, soil depths and their interaction significantly influenced H´, λ, WI, PPI (index of plant parasites), MI (maturation index excluding plant parasites), PPI/MI, F/B and NCR. The Shannon index (H´) was higher in the 10-year cotton field than in the other-year fields. The Simpson index (λ) was the lowest in the 10-year cotton field. The lowest value of WI (index of Wasilewska) appeared at the 20-year cotton field, which had the majority of plant parasites. Increases of cotton cropping times determined a decreased trend of NCR [=B/(B + F)], and an increased trend of F/B [F and B represent the consumer abundance of fungi (F) and bacteria (B)]. The bacterial decomposition pathway was more important in the 5-year situations, and the fungal decomposition pathway was more important in the 20-year situations. Nematode analysis showed that changes of soil nematode communities and trophic groups could indicate changes in the soil environment and nematode community structure with changes of continuous cropping times.